Systems and methods for determining engagement of a portable device

ABSTRACT

A portable device is provided having a motion sensor and an engagement sensor. A determination may be made whether the portable device is engaged with the platform. The data being output by the sensor may be used accordingly.

FIELD OF THE PRESENT DISCLOSURE

This disclosure generally relates to assessing characteristics of theassociation between a platform and a portable device, and morespecifically to determining whether a wearable device is engaged with auser and interpreting data collected from a health monitoring sensor ofthe wearable device based at least in part on the determined engagement.

BACKGROUND

Developments in sensor technology, such as the use ofmicroelectromechanical systems (MEMS), have enabled the incorporation ofa wide variety of sensors into mobile devices. Non-limiting examples ofsuch sensors include an accelerometer, a gyroscope, a magnetometer, apressure sensor, a microphone, a proximity sensor, an ambient lightsensor, an infrared sensor, and the like. One or more of these sensors,or others, may be used for a similarly wide variety of purposes,including monitoring, characterizing or analyzing quantities related tothe health of a user. As an illustrative example only and withoutlimitation, a health sensor may be a photoplethysmograph used todetermine the pulse rate and/or blood oxygen saturation of a user bysensing changes in the amount of light absorbed by tissue. Accordingly,the quality of the data provided by the photoplethysmograph may dependon how securely the sensor is engaged with the user, otherwise movementof the sensor with respect to the user may produce erroneous signalcomponents, such as may be attributed to varying amounts of ambientlight being recorded. It should be appreciated that many other types ofsensors may also be influenced by how a portable device incorporatingthem are associated with a platform, such as a user.

In light of these observations, it would be desirable to assess one ormore characteristics of the association between a user and a portabledevice. For example, it would be desirable to determine whether awearable device is engaged with a user, allowing the data being outputby the sensor to be interpreted more accurately. Further, it would bedesirable to validate data output by a sensor when it is determined thewearable device is engaged with the user. Still further, it would bedesirable to utilize different algorithms or otherwise adjust theanalysis of sensor data depending on whether the wearable device isengaged with the user or not. More generally, it would be desirable touse the determination of the engagement of any portable device with aplatform when using sensor data, such as for aiding a navigationalsolution that uses motion sensor data provided by the portable device.The techniques of this disclosure satisfy these and other needs asdescribed in the following materials. While the following discussion isin the context of MEMS sensors as used in portable devices, one of skillin the art will recognize that these techniques may be employed to anysuitable sensor application as desired.

SUMMARY

This disclosure is directed to a method for determining engagement of aportable device with a platform. The method may involve obtaining motionsensor data for the portable device, obtaining engagement sensor datafor the portable device and determining the portable device isexhibiting motion with respect to the platform when the engagementsensor data exceeds an engagement threshold, wherein the engagementthreshold is based at least in part on the motion sensor data.

This disclosure also includes a portable device having a motion sensor,an engagement sensor and an engagement module configured to compare datafrom the engagement sensor to an engagement threshold, wherein theengagement threshold is based at least in part on data output by themotion sensor, and to determine the portable device is exhibiting motionwith respect to a platform when the engagement sensor data exceeds anengagement threshold.

Still further, this disclosure includes a system for determiningengagement of a portable device with a platform. The system may includea portable device having a motion sensor and an engagement sensor and anauxiliary device having an engagement module. The auxiliary device mayreceive data from the motion sensor and the engagement sensor such thatthe engagement module may compare data from the engagement sensor to anengagement threshold, wherein the engagement threshold is based at leastin part on data output by the motion sensor, and may determine theportable device is exhibiting motion with respect to a platform when theengagement sensor data exceeds an engagement threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a photoplethysmograph in accordancewith an embodiment.

FIG. 2 is a high level schematic diagram of a portable device configuredas a photoplethysmograph in accordance with an embodiment.

FIG. 3 depicts a routine representing the operations of an engagementmodule in accordance with an embodiment.

FIG. 4 depicts test data showing accelerometer data and proximity dataused in making a determination of not engaged in accordance with anembodiment.

FIG. 5 depicts test data showing accelerometer data and proximity dataused in making a determination of engaged in accordance with anembodiment.

DETAILED DESCRIPTION

At the outset, it is to be understood that this disclosure is notlimited to particularly exemplified materials, architectures, routines,methods or structures as such may vary. Thus, although a number of suchoptions, similar or equivalent to those described herein, can be used inthe practice or embodiments of this disclosure, the preferred materialsand methods are described herein.

It is also to be understood that the terminology used herein is for thepurpose of describing particular embodiments of this disclosure only andis not intended to be limiting.

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of thepresent disclosure and is not intended to represent the only exemplaryembodiments in which the present disclosure can be practiced. The term“exemplary” used throughout this description means “serving as anexample, instance, or illustration,” and should not necessarily beconstrued as preferred or advantageous over other exemplary embodiments.The detailed description includes specific details for the purpose ofproviding a thorough understanding of the exemplary embodiments of thespecification. It will be apparent to those skilled in the art that theexemplary embodiments of the specification may be practiced withoutthese specific details. In some instances, well known structures anddevices are shown in block diagram form in order to avoid obscuring thenovelty of the exemplary embodiments presented herein.

For purposes of convenience and clarity only, directional terms, such astop, bottom, left, right, up, down, over, above, below, beneath, rear,back, and front, may be used with respect to the accompanying drawingsor chip embodiments. These and similar directional terms should not beconstrued to limit the scope of the disclosure in any manner.

In this specification and in the claims, it will be understood that whenan element is referred to as being “connected to” or “coupled to”another element, it can be directly connected or coupled to the otherelement or intervening elements may be present. In contrast, when anelement is referred to as being “directly connected to” or “directlycoupled to” another element, there are no intervening elements present.

Some portions of the detailed descriptions which follow are presented interms of procedures, logic blocks, processing and other symbolicrepresentations of operations on data bits within a computer memory.These descriptions and representations are the means used by thoseskilled in the data processing arts to most effectively convey thesubstance of their work to others skilled in the art. In the presentapplication, a procedure, logic block, process, or the like, isconceived to be a self-consistent sequence of steps or instructionsleading to a desired result. The steps are those requiring physicalmanipulations of physical quantities. Usually, although not necessarily,these quantities take the form of electrical or magnetic signals capableof being stored, transferred, combined, compared, and otherwisemanipulated in a computer system.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout the present application,discussions utilizing the terms such as “accessing,” “receiving,”“sending,” “using,” “selecting,” “determining,” “normalizing,”“multiplying,” “averaging,” “monitoring,” “comparing,” “applying,”“updating,” “measuring,” “deriving” or the like, refer to the actionsand processes of a computer system, or similar electronic computingdevice, that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

Embodiments described herein may be discussed in the general context ofprocessor-executable instructions residing on some form ofnon-transitory processor-readable medium, such as program modules,executed by one or more computers or other devices. Generally, programmodules include routines, programs, objects, components, datastructures, etc., that perform particular tasks or implement particularabstract data types. The functionality of the program modules may becombined or distributed as desired in various embodiments.

In the figures, a single block may be described as performing a functionor functions; however, in actual practice, the function or functionsperformed by that block may be performed in a single component or acrossmultiple components, and/or may be performed using hardware, usingsoftware, or using a combination of hardware and software. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure. Also, the exemplary wirelesscommunications devices may include components other than those shown,including well-known components such as a processor, memory and thelike.

The techniques described herein may be implemented in hardware,software, firmware, or any combination thereof, unless specificallydescribed as being implemented in a specific manner. Any featuresdescribed as modules or components may also be implemented together inan integrated logic device or separately as discrete but interoperablelogic devices. If implemented in software, the techniques may berealized at least in part by a non-transitory processor-readable storagemedium comprising instructions that, when executed, performs one or moreof the methods described above. The non-transitory processor-readabledata storage medium may form part of a computer program product, whichmay include packaging materials.

The non-transitory processor-readable storage medium may comprise randomaccess memory (RAM) such as synchronous dynamic random access memory(SDRAM), read only memory (ROM), non-volatile random access memory(NVRAM), electrically erasable programmable read-only memory (EEPROM),FLASH memory, other known storage media, and the like. The techniquesadditionally, or alternatively, may be realized at least in part by aprocessor-readable communication medium that carries or communicatescode in the form of instructions or data structures and that can beaccessed, read, and/or executed by a computer or other processor. Forexample, a carrier wave may be employed to carry computer-readableelectronic data such as those used in transmitting and receivingelectronic mail or in accessing a network such as the Internet or alocal area network (LAN). Of course, many modifications may be made tothis configuration without departing from the scope or spirit of theclaimed subject matter.

The various illustrative logical blocks, modules, circuits andinstructions described in connection with the embodiments disclosedherein may be executed by one or more processors, such as one or moredigital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), application specificinstruction set processors (ASIPs), field programmable gate arrays(FPGAs), or other equivalent integrated or discrete logic circuitry. Theterm “processor,” as used herein may refer to any of the foregoingstructure or any other structure suitable for implementation of thetechniques described herein. In addition, in some aspects, thefunctionality described herein may be provided within dedicated softwaremodules or hardware modules configured as described herein. Also, thetechniques could be fully implemented in one or more circuits or logicelements. A general purpose processor may be a microprocessor, but inthe alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one having ordinaryskill in the art to which the disclosure pertains.

Finally, as used in this specification and the appended claims, thesingular forms “a, “an” and “the” include plural referents unless thecontent clearly dictates otherwise.

As noted above, the techniques of this disclosure may be used todetermine whether a portable device is engaged with a platform and usingdata being output by the sensor accordingly. For example, data output bya sensor may be validated when it is determined a wearable device isengaged with a user. Alternatively or in addition, different algorithmsmay be employed or other processing techniques may be applied dependingon whether the wearable device is engaged with the user or not. Moregenerally, a determination of the engagement of a portable device with aplatform may be used for other purposes, such as for aiding anavigational solution that uses motion sensor data provided by theportable sensor.

To help illustrate aspects of this disclosure, FIG. 1 schematicallydepicts a photoplethysmograph and the corresponding data output. In thisembodiment, photoplethysmograph 10 is configured as a portable, wearabledevice that may be worn on a user's finger 12 as shown. Other designsmay be adapted as warranted depending on where the photoplethysmographis to be worn, such as an ear lobe, a wrist or any other suitablelocation. Although a photoplethysmograph is the health sensor describedin this embodiment, any other health or biophysical sensor such aselectrocardiogram patches or other electrical sensors, blood pressuremonitors, or ultrasound monitors for example are within the context ofthe disclosure. Further, these techniques may also be applied to anytype of sensor that may incorporated into a portable device if thesensor is influenced by the association between the portable device andits conveying platform. As an illustrative example only, a portabledevice may have one or more motion sensors which may output data that isinterpreted in light of an assessment of the engagement between theportable device and a platform, which may be a user, a vehicle or othermoving element. Correspondingly, a navigation solution derived for theportable device may be aided by considering the engagement with theplatform, as the motion sensor data may correspond more directly withmotion of the platform when the portable device is engaged with theplatform.

The components of photoplethysmograph 10 used to monitor aspects of auser's cardiovascular system include a light source 14, typicallyinfrared and/or red, and a light sensor 16. In one embodiment, lightsource 14 may be a green light emitting diode (LED). Light emitted bylight source 14 transmitted through and/or reflected by the tissue inthe user's finger 12 may be absorbed to varying degrees. Skin, bone andother tissue, as well as venous blood, represents a substantiallyconstant absorption that is unrelated to the user's heart rate. As such,a direct current (DC) signal component is present in the output of lightsensor 16 as indicated. In contrast, the arterial blood volume changesin coordination with the user's heart rate, resulting in an alternatingcurrent (AC) signal component. The characteristics of the AC signalcorrespond to features of the heart rate, such by exhibiting maxima andminima at the systolic point 18 and the diastolic point 20,respectively, with an intermediate dicrotic notch 22. The period betweensequential features may be calculated to provide an accurate measure ofthe user's heart rate.

As will be appreciated, when photoplethysmograph 10 is engaged withfinger 12, the ambient light received by light sensor 16 will remainmore constant. Further, engagement of photoplethysmograph 10 with finger12 will also maintain the relationship of light source 14 and lightsensor 16 with the tissue of finger 12, so that the path traveled by thelight as it reflects through and/or is transmitted by the tissue alsoremains more constant. In turn, these characteristics help stabilize theDC component of the signal received by light sensor 16 so that thevariable AC component more accurately reflects the changes in arterialblood due to the user's heart rate. Conversely, when photoplethysmograph10 is not engaged with finger 12, the amount of ambient light to whichlight sensor 16 is exposed may vary, degrading the quality of the ACsignal component. Similarly, changes in the relationship between lightsource 14 and light sensor 16 with the tissue of finger 12 may alsochange the amount of light absorbed by non-pulsatile components, alsodegrading signal quality.

Accordingly, the techniques of this disclosure may include providingphotoplethysmograph 10 with an engagement sensor in order to determinecharacteristics of the association with the user. One exemplaryembodiment is depicted with high level schematic blocks in FIG. 2. Aswill be appreciated, photoplethysmograph 10 may be implemented as adevice or apparatus, such as a wearable device designed to positionlight source 14 and light sensor 16 at a desired location of the user,such as a fingertip, an ear lobe, a wrist or any other suitablelocation. In other embodiments, any portable device that can be moved inspace by a user and its motion, location and/or orientation in spacetherefore sensed may be employed. For example, such a portable devicemay be a mobile phone (e.g., smartphone, cellular phone, a phone runningon a local network, or any other telephone handset), tablet, personaldigital assistant (PDA), video game player, video game controller,navigation device, wearable device (e.g., glasses, watch, belt clip,ring, garment, shoe), fitness tracker, virtual or augmented realityequipment, mobile internet device (MID), personal navigation device(PND), digital still camera, digital video camera, binoculars, telephotolens, portable music, video or media player, remote control, or otherhandheld device, or a combination of one or more of these devices.Similarly, the portable device may have any combination of healthsensors or other types of sensors that may benefit from thedetermination of whether the portable device is engaged with a platform.

As shown, photoplethysmograph 10 includes a host processor 24, which maybe one or more microprocessors, central processing units (CPUs), orother processors to run software programs, which may be stored in memory26, associated with the functions of photoplethysmograph 10. Multiplelayers of software can be provided in memory 26, which may be anycombination of computer readable medium such as electronic memory orother storage medium such as hard disk, optical disk, etc., for use withthe host processor 24. For example, an operating system layer can beprovided for photoplethysmograph 10 to control and manage systemresources in real time, enable functions of application software andother layers, and interface application programs with other software andfunctions of photoplethysmograph 10. Similarly, different softwareapplication programs such as menu navigation software, games, camerafunction control, navigation software, communications software, such astelephony or wireless local area network (WLAN) software, or any of awide variety of other software and functional interfaces can beprovided. In some embodiments, multiple different applications can beprovided on a single photoplethysmograph 10, and in some of thoseembodiments, multiple applications can run simultaneously.

Photoplethysmograph 10 includes at least one sensor assembly, as shownhere in the form of integrated motion processing unit (MPU™) 28featuring sensor processor 30, memory 32 and inertial sensor 34. Memory32 may store algorithms, routines or other instructions for processingdata output by inertial sensor 34 and/or other sensors as describedbelow using logic or controllers of sensor processor 30, as well asstoring raw data and/or motion data output by inertial sensor 34 orother sensors. Inertial sensor 34 may be one or more sensors formeasuring motion of photoplethysmograph 10 in space. Depending on theconfiguration, MPU 28 measures one or more axes of rotation and/or oneor more axes of acceleration of the device. In one embodiment, inertialsensor 34 may include rotational motion sensors or linear motionsensors. For example, the rotational motion sensors may be gyroscopes tomeasure angular velocity along one or more orthogonal axes and thelinear motion sensors may be accelerometers to measure linearacceleration along one or more orthogonal axes. In one aspect, threegyroscopes and three accelerometers may be employed, such that a sensorfusion operation performed by sensor processor 30, or other processingresources of photoplethysmograph 10, combines data from inertial sensor34 to provide a six axis determination of motion. As desired, inertialsensor 34 may be implemented using Micro Electro Mechanical System(MEMS) to be integrated with MPU 28 in a single package. Exemplarydetails regarding suitable configurations of host processor 24 and MPU28 may be found in co-pending, commonly owned U.S. patent applicationSer. No. 11/774,488, filed Jul. 6, 2007, and Ser. No. 12/106,921, filedApr. 11, 2008, which are hereby incorporated by reference in theirentirety. Suitable implementations for MPU 28 in photoplethysmograph 10are available from InvenSense, Inc. of Sunnyvale, Calif.

Alternatively or in addition, photoplethysmograph 10 may implement asensor assembly in the form of external sensor 36. This is optional andnot required in all embodiments. External sensor 36 may represent one ormore sensors as described above, such as an accelerometer and/or agyroscope, or any other suitable sensor configured to measure one ormore aspects about the environment surrounding device 16. This isoptional and not required in all embodiments. As used herein, “external”means a sensor that is not integrated with MPU 28 and may be remote orlocal to photoplethysmograph 10. For example, a barometer and/or amagnetometer may be used to refine position determinations made usinginertial sensor 34. In one embodiment, external sensor 36 may include amagnetometer measuring along three orthogonal axes and output data to befused with the gyroscope and accelerometer inertial sensor data toprovide a nine axis determination of motion. In another embodiment,external sensor 36 may also include a barometer to provide an altitudedetermination that may be fused with the other sensor data to provide aten axis determination of motion. Although described in the context ofone or more sensors being MEMS based, the techniques of this disclosuremay be applied to any sensor design or implementation.

In the embodiment shown, host processor 24, memory 26, MPU 28 and othercomponents of photoplethysmograph 10 may be coupled through bus 38,which may be any suitable bus or interface, such as a peripheralcomponent interconnect express (PCIe) bus, a universal serial bus (USB),a universal asynchronous receiver/transmitter (UART) serial bus, asuitable advanced microcontroller bus architecture (AMBA) interface, anInter-Integrated Circuit (I2C) bus, a serial digital input output (SDIO)bus, a serial peripheral interface (SPI) or other equivalent. Dependingon the architecture, different bus configurations may be employed asdesired. For example, additional buses may be used to couple the variouscomponents of photoplethysmograph 10, such as by using a dedicated busbetween host processor 24 and memory 26.

As noted above, photoplethysmograph 10 also includes an engagementsensor 40. Depending on the implementation, engagement sensor 40 may bea proximity sensor, a distance sensor or any other sensor that outputs asignal corresponding to the range between photoplethysmograph 10 and anadjacent object. Engagement sensor 40 may detect changes in anelectromagnetic field to determine whether an object is adjacent thesensor. In other embodiments, other quantities may be measured todetermine the relative distance to an object, including sound wavesusing an ultrasonic transducer, for example. Engagement sensor 40 may becoupled to bus 38, may be coupled to MPU 28 as with external sensor 36,or may be implemented using any other suitable architecture. Further, insome embodiments, light source 14 and light sensor 16 may be used toprovide the functionality of an engagement sensor. As discussed above, alack of engagement between photoplethysmograph 10 and finger 12 mayresult in variation in the DC signal component. Photoplethysmograph 10may be configured with a feedback loop to provide a desired stable DCsignal component by altering the current used to drive light source 14.Correspondingly, the drive current may be sampled, such as with ananalog to digital converter (ADC) to provide a signal that representsengagement between photoplethysmograph 10 and finger 12. For example, arelatively more constant drive current may indicate engagement while arelatively more variable drive current may indicate a lack ofengagement. Reference values may be established as warranted duringcalibration of photoplethysmograph 10.

In this exemplary system, photoplethysmograph 10 communicates raw sensordata at least with regard to inertial sensor 34 and engagement sensor 40to auxiliary device 42, which may include processor 44 that is incommunication with memory 46 over bus 48. Auxiliary device 42 mayoperate in conjunction with photoplethysmograph 10, such as by providinga more convenient user interface and/or increased processing resources.As an illustration, auxiliary device 42 may be a smartphone. Processor44 may execute instructions stored in memory 46 that are represented asfunctional blocks, including engagement module 48, which may perform theoperations described in this disclosure to characterize the associationbetween a portable device, such as photoplethysmograph 10, and aplatform, such as a user. Auxiliary device 42 may also include acommunications module 50 to receive raw sensor data sent bycommunications module 52 of photoplethysmograph 10. The communicationsmodules may employ any suitable protocol, including a shorter range, lowpower communication protocol such as BLUETOOTH®, ZigBee®, ANT or alonger range communication protocol, such as a transmission controlprotocol, internet protocol (TCP/IP) packet-based communication,accessed using a wireless local area network (WLAN), cell phone protocolor the like. In other embodiments, a wired connection may be employed.In general, the system depicted in FIG. 2 may embody aspects of anetworked or distributed computing environment. Photoplethysmograph 10and auxiliary device 42 may communicate either directly or indirectly,such as through multiple interconnected networks. As will beappreciated, a variety of systems, components, and networkconfigurations, topologies and infrastructures, such as client/server,peer-to-peer, or hybrid architectures, may be employed to supportdistributed computing environments.

Multiple layers of software may be employed as desired and stored in anycombination of memory 26, memory 32, memory 46, or other suitablelocation. For example, a motion algorithm layer can provide motionalgorithms that provide lower-level processing for raw sensor dataprovided from the motion sensors and other sensors. A sensor devicedriver layer may provide a software interface to the hardware sensors ofphotoplethysmograph 10. Further, a suitable application programinterface (API) may be provided to facilitate communication between hostprocessor 24 and MPU 28, for example, to transmit desired sensorprocessing tasks. Similarly, any suitable division of processingresources may be employed whether within photoplethysmograph 10,auxiliary device 42, or among any plurality of other devices. Forexample, processor 44 may receive sensor data from light sensor 16 usingcommunication module 50 and execute instructions from engagement module48 to determine engagement between photoplethysmograph 10 and the user.In turn, the engagement information may be communicated tophotoplethysmograph 10 for use in processing data, such as by processor24. Alternatively, processor 44 may also receive output from lightsensor 16 and process the data locally. Further, aspects implemented insoftware may include but are not limited to, application software,firmware, resident software, microcode, etc., and may take the form of acomputer program product accessible from a non-transitorycomputer-usable or computer-readable medium providing program code foruse by or in connection with a computer or any instruction executionsystem, such as host processor 24, sensor processor 30, processor 44, adedicated processor or any other processing resources ofphotoplethysmograph 10, auxiliary device 42 or other remote processingresources, or may be implemented using any desired combination ofsoftware, hardware and firmware. Further, any or all of the functionsmay be performed by photoplethysmograph 10 itself, such as byimplementing engagement module 48 in memory 26 or any other suitablesystem architecture.

Correspondingly, engagement of a portable device, such asphotoplethysmograph 10, with a platform, such as a user, may includesampling data from inertial sensor 34 and engagement sensor 40 anddetermining the portable device is exhibiting motion with respect to theplatform when the motion sensor data exceeds a motion threshold when theengagement sensor data exceeds an engagement threshold. In someembodiments, photoplethysmograph 10 may include indicator 54 tocommunicate to a user the determination provided by engagement module48, allowing the user to adjust the positioning or connection ofphotoplethysmograph 10. Any suitable indication may be used, includingvisual, auditory or tactile. For example, photoplethysmograph 10 mayhave a display provided as part of the user interface which may functionas indicator 54. Alternatively, a dedicated light or the like may beused to signal engagement. In other embodiments, an indicator may beprovided on auxiliary device 42 in a similar manner.

A representative routine of the operations performed by engagementmodule 48 is depicted in FIG. 3. Beginning with 60, motion sensor datamay be obtained for a plurality of epochs over a given time period, suchas from inertial sensor 34 and/or external sensor 36, forphotoplethysmograph 10. In this embodiment, sensor data is provided forthree orthogonal axes, x, y and z, although fewer axes may be employedor may be combined, and may be obtained from a gyroscope, anaccelerometer, or another suitable motion sensor. In 62, engagementsensor data is obtained, such as from engagement sensor 40 or from theoperation of light source 14 and light sensor 16 as described above. Theintensity of motion experienced by photoplethysmograph 10 is determinedby computing a norm of the motion sensor data, such as the Euclidian,distance or 2-norm, in 64. The variance of the engagement sensor data isdetermined in 66, and may be assessed over an adaptive window ofsamples. The size of the window may be adjusted in 68 based on the normof the motion sensor data, typically by correlating the size of thewindow with the intensity of motion as determined from the norm. Basedat least in part on motion intensity and engagement sensor variance, asuitable engagement threshold may also be set in 68. Correspondingly,the variance of the engagement sensor data is compared to the engagementthreshold in 70, with a engaged or not engaged determination returnedfor the current epoch. In 72, a voting window may be employed to helpreduce the risk of a false positive by accumulating results over aseries of epochs. The output of 72 may indicate whether engaged or notengaged depending on the majority (or a more stringent test if desired)of determinations over the voting window. In some embodiments, it may bedesirable to return a result of no determination if the voting isinconclusive.

As an example only and without limitation, motion sensor data may besampled at 25 Hz and the norm calculated for the preceding 32 samples.Engagement sensor 40 may be polled at the same rate with an initialwindow of 64 samples, that may be adjusted up or down depending on thenorm of the motion sensor data. A voting window of five epochs may beemployed. In some embodiments, it may be desirable to conserve power bynot sampling engagement sensor 40 until the sensed motion exceeds asuitable threshold.

To help illustrate application of these techniques, tests were conductedand the results are depicted in FIGS. 4 and 5. In each figure, the topgraph shows the output of inertial sensor 34, which is an accelerometerin this embodiment. The middle graph shows the output of the engagementsensor 40, a proximity sensor in this embodiment. The bottom graph showsthe output of voting window 72, with an engaged determinationrepresented by 1 and a not engaged determination represented by 2. Fromthese results, it may be possible to make a not engaged determinationwith approximately 90% confidence and an engaged determination withapproximately 95% confidence.

In one aspect, the motion sensor data may be accelerometer data.

In one aspect, the motion sensor data may be gyroscope data.

In one aspect, the engagement sensor is selected from the groupconsisting of a proximity sensor and a distance sensor.

In one aspect, the engagement sensor may be a light sensor.

In one aspect, the engagement threshold may be based at least in part ona norm of the motion sensor data over a window of sequential samples.The engagement threshold may be positively correlated with the norm ofthe motion sensor data. The method may also involve adjusting a size ofthe window of sequential samples. The size of the window of sequentialsamples may be positively correlated with an amount of motion indicatedby the motion sensor data.

In one aspect, the portable device may be a health sensor and whereinthe platform is a user. The health sensor may be a photoplethysmographsensor, further comprising determining validity for photoplethysmographsensor data based at least in part on whether the portable device isexhibiting motion with respect to the user. The method may also involveemploying an algorithm to evaluate photoplethysmograph sensor data thatis based at least in part on whether the portable device is exhibitingmotion with respect to the user. An indication may be provided to theuser whether the engagement sensor data exceeds an engagement threshold

In one aspect, the method may involve employing an algorithm to providea navigation solution for the portable device that is based at least inpart on whether the portable device is exhibiting motion with respect tothe user.

In the described embodiments, an electronic device incorporating asensor may employ a motion tracking module also referred to as MotionProcessing Unit (MPU) that includes at least one sensor in addition toelectronic circuits. The sensor, such as a gyroscope, a compass, amagnetometer, an accelerometer, a microphone, a pressure sensor, aproximity sensor, or an ambient light sensor, among others known in theart, are contemplated. Some embodiments include accelerometer,gyroscope, and magnetometer, which each provide a measurement alongthree axes that are orthogonal relative to each other referred to as a9-axis device. Other embodiments may not include all the sensors or mayprovide measurements along one or more axes. The sensors may be formedon a first substrate. Other embodiments may include solid-state sensorsor any other type of sensors. The electronic circuits in the MPU receivemeasurement outputs from the one or more sensors. In some embodiments,the electronic circuits process the sensor data. The electronic circuitsmay be implemented on a second silicon substrate. The first substratemay be vertically stacked, attached and electrically connected to thesecond substrate in a single semiconductor chip.

In one embodiment, the first substrate is attached to the secondsubstrate through wafer bonding, as described in commonly owned U.S.Pat. No. 7,104,129, which is incorporated herein by reference in itsentirety, to simultaneously provide electrical connections andhermetically seal the MEMS devices. This fabrication techniqueadvantageously enables technology that allows for the design andmanufacture of high performance, multi-axis, inertial sensors in a verysmall and economical package. Integration at the wafer-level minimizesparasitic capacitances, allowing for improved signal-to-noise relativeto a discrete solution. Such integration at the wafer-level also enablesthe incorporation of a rich feature set which minimizes the need forexternal amplification.

In the described embodiments, raw data refers to measurement outputsfrom the sensors which are not yet processed. Motion data refers toprocessed raw data. Processing may include applying a sensor fusionalgorithm or applying any other algorithm. In the case of the sensorfusion algorithm, data from one or more sensors are combined to providean orientation of the device. In the described embodiments, a MPU mayinclude processors, memory, control logic and sensors among structures.

Although the present invention has been described in accordance with theembodiments shown, one of ordinary skill in the art will readilyrecognize that there could be variations to the embodiments and thosevariations would be within the spirit and scope of the presentinvention. Accordingly, many modifications may be made by one ofordinary skill in the art without departing from the spirit and scope ofthe present invention.

What is claimed is:
 1. A method for determining engagement of a portable device with a platform, comprising: obtaining motion sensor data for the portable device; obtaining engagement sensor data for the portable device; and determining the portable device is exhibiting motion with respect to the platform when the engagement sensor data exceeds an engagement threshold, wherein the engagement threshold is based at least in part on the motion sensor data.
 2. The method of claim 1, wherein the motion sensor data comprises accelerometer data.
 3. The method of claim 1, wherein the motion sensor data comprises gyroscope data.
 4. The method of claim 1, wherein the engagement sensor is selected from the group consisting of a proximity sensor and a distance sensor.
 5. The method of claim 1, wherein the engagement sensor comprises a light sensor.
 6. The method of claim 1, wherein the engagement threshold is based at least in part on a norm of the motion sensor data over a window of sequential samples.
 7. The method of claim 6, wherein the engagement threshold is positively correlated with the norm of the motion sensor data.
 8. The method of claim 6, further comprising adjusting a size of the window of sequential samples.
 9. The method of claim 8, wherein the size of the window of sequential samples is positively correlated with an amount of motion indicated by the motion sensor data.
 10. The method of claim 1, wherein the portable device comprises a health sensor and wherein the platform is a user.
 11. The method of claim 10, wherein the health sensor comprises a photoplethysmograph sensor, further comprising determining validity for photoplethysmograph sensor data based at least in part on whether the portable device is exhibiting motion with respect to the user.
 12. The method of claim 11, further comprising employing an algorithm to evaluate photoplethysmograph sensor data that is based at least in part on whether the portable device is exhibiting motion with respect to the user.
 13. The method of claim 1, further comprising employing an algorithm to provide a navigation solution for the portable device that is based at least in part on whether the portable device is exhibiting motion with respect to the user.
 14. The method of claim 1, further comprising providing an indication to the user whether the engagement sensor data exceeds an engagement threshold.
 15. A portable device, comprising: a motion sensor; an engagement sensor; and an engagement module configured to compare data from the engagement sensor to an engagement threshold, wherein the engagement threshold is based at least in part on data output by the motion sensor, and to determine the portable device is exhibiting motion with respect to a platform when the engagement sensor data exceeds an engagement threshold.
 16. The portable device of claim 15, wherein the motion sensor comprises an accelerometer.
 17. The portable device of claim 15, wherein the motion sensor comprises a gyroscope.
 18. The portable device of claim 15, wherein the engagement sensor is selected from the group consisting of a proximity sensor and a distance sensor.
 19. The portable device of claim 15, wherein the engagement sensor comprises a light sensor.
 20. The portable device of claim 15, wherein the engagement threshold is based at least in part on a norm of the motion sensor data over a window of sequential samples.
 21. The portable device of claim 20, wherein the engagement threshold is positively correlated with the norm of the motion sensor data.
 22. The portable device of claim 20, wherein the engagement module is further configured to adjust a size of the window of sequential samples.
 23. The portable device of claim 22, wherein the size of the window of sequential samples is positively correlated with an amount of motion indicated by the motion sensor data.
 24. The portable device of claim 15, wherein the portable device comprises a health sensor and wherein the platform is a user.
 25. The portable device of claim 24, wherein the engagement module is further configured to provide an indication to the user when the engagement sensor data exceeds an engagement threshold.
 26. The portable device of claim 24, wherein the health sensor comprises a photoplethysmograph sensor, wherein the engagement module is further configured to determine validity for photoplethysmograph sensor data based at least in part on whether the portable device is exhibiting motion with respect to the user.
 27. The portable device of claim 26, wherein the engagement module is further configured to employ an algorithm to evaluate photoplethysmograph sensor data that is based at least in part on whether the portable device is exhibiting motion with respect to the user.
 28. The portable device of claim 15, wherein the engagement module is further configured to employ an algorithm to provide a navigation solution for the portable device that is based at least in part on whether the portable device is exhibiting motion with respect to the platform.
 29. A system comprising a portable device, wherein the portable device comprises a motion sensor and an engagement sensor, and an auxiliary device comprising an engagement module, wherein the auxiliary device receives data from the motion sensor and the engagement sensor and wherein the engagement module compares data from the engagement sensor to an engagement threshold, wherein the engagement threshold is based at least in part on data output by the motion sensor, and determines the portable device is exhibiting motion with respect to a platform when the engagement sensor data exceeds an engagement threshold. 